Make it make sense
Make it make sense
170 comments
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Most traffic jams actually act as a kind of compression wave moving backwards through traffic. Something as small as a squirrel running across the road can cascade into an hour-long jam.
One person brakes, then the person behind them, then the person behind them, but each time they are getting closer to each other (nobody stays equidistant from the car in front of them when braking). This causes a greater and greater slowdown as more cars are compacted into a tighter space, which travels backwards in traffic like a wave. Often the person who caused it doesn't even realize anything happened.
A lot of mapping software actually estimates a given traffic slowdown by treating traffic as a fluid with a wave moving backwards through it.
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That's also why the best way to relieve traffic is to go at a slow even pace without braking. Every time the someone in heavy traffic runs up the ass of another car and brakes hard, or swerves into the "faster" lane and make someone else brake to not hit them, they cause another brake wave. If you have a few cars intentionally just hanging back and cruising with a big enough gap between them and the cars jocking for position in traffic in front of them, then their brake waves do not propogate behind you and eventually traffic just picks up pace again.
Edit: side bonus, you still get there just as fast, but with a lot less stress fighting assholes for position (minus the ones who fly past you thinking you're the asshole for not riding someone else's bumper)
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Nicely demonstrated here: https://youtu.be/Suugn-p5C1M
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Californians te the worst drivers in the world because none of them understand this simple concept. Every day I’m driving, I give more than enough space in front of me for someone to cut me off and I don’t have to brake. It’s simple. However, I’m constantly getting people riding my ass. Switching around me. And being over all menaces just because I’m leaving a roper gap between myself and the car in front of me. It’s wild.
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Right, if you think about the creation of traffic as a negative speed wave which causes compression, and traffic alleviation as a positive speed wave which requires rarefaction, then it becomes clear why traffic is so stubborn. When people are so bunched together, no positive speed wave can propagate. Which is why you literally get to to the point where the original idiot slammed on the brakes and the traffic magically disintegrates. If everyone stayed 5 car lengths apart in traffic, that alleviation would actually propagate backwards as fast as the initial congestion.
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Preach truth, Krypty
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Do you know of a paper that describes this kind of traffic motion?
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Here's the (abstract of the) paper I was thinking of https://pubsonline.informs.org/doi/abs/10.1287/opre.4.1.42
Appalling that I can't find a free version of a 70 year old paper. You might be able to find the full text somewhere... I would of course never encourage anything that might run afoul of the scientific publishing protection racket.
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I couldn't find the paper I was thinking of that described the phenomenon of traffic propagating as a pressure wave, but I did find this paper (new to me) that describes a model for simulating how congestion spreads in urban environments (as opposed to an isolated highway, which IIRC the paper that most people reference models). It does have the full text available though, and it looks like a good read and has references that should get you going on the history of congestion research.
I am not an expert; I just found this with a few minutes of searching. If there are experts with better papers I'd be happy to hear from ya!
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I knew about the elastic band effect, but I was unsure if it was considered the same. But searching that I found about both:
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In one of the Mission Impossible movies Tom Cruise is supposed to have a boring job no one will ask him about and the movie shows this by having the character talk about traffic patterns. I thought it was interesting information then and think it is interesting now.
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A few years ago, I was removed and moaning about a jam, and my pal just said "you're not in traffic, you are traffic".
I know it's nothing more than a cheeky soundbite but just reframing it like that and knowing I'm part of the problem rather than the exception has made me a lot calmer on slow moving roads.
Plus it has encouraged me to either use public transport more, or just drive to a park-and-ride a mile or three out, and run the rest - facilities permitting of course.
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Yeah that was a through the matrix moment for me too.
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I still lose it when I finally get to the front of the jam, and the only reason for said jam is because everyone is stopping to look at an accident on the OTHER SIDE OF THE HIGHWAY.
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Yeah, it's frustrating.
I'm not entirely sure what the rubberneckers want to see either. "Oh look, someone critically injured next to someone who is likely deceased", because that isn't a day ruiner at the best of times.
Odd.
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Only ever have to ask, my friend
Heres an overview shot of a traffic pulse.
One person brakes for no reason which leads to everyone else braking. The pulse travels despite there being nothing there. The longer it can take for someone to start up again also can delay the whole thing.
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It happens when people tailgate. They over react and it causes an accordion effect.
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Or when people drive too aggressively and cut someone off, causing the person being cut off to slam on their brake.
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Iirc, the answer is to have someone drive slowly and let other cars pass. It creates a buffer zone that regulates the flow back to normal pace. Or at least that's what I remember from New Scientist's video from like a decade ago.
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I used to just idle when traffic moved. Slowed down way before i was even close to the car ahead. Played a game where i was trying to move at a constant speed or max fuel econ. Much less stressful to always be moving than gas/brake every 10s, even if you're moving 5mph.
Really helps to look 3-4 cars ahead for brake lights.
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not slowly, just leave room
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Nope that's just a negative picture of a guy
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Hey I studied this in grad school for a bit, and it really is just "someone does some dumb shit which leads to a cascading wave of additional people doing dumb shit which propagates backwards for miles." Basically when the offered load is getting close to the maximum load, all it takes is one person aggressively changing lanes to throw that section of highway into gridlock, and it will remain that way until the total integrated traffic flux across that incident boundary again falls below the critical offered load inflection point.
Basically, pick a lane and just stay in it. Maintain proper following distance. Counterintuitively, the following distance should be for the speed you want to drive, so even in traffic it should be like 5+ car lengths even though you are going slow. This is because it reduces the offered load, and once that number falls below the critical point, speeds will increase again. Bumper to bumper traffic basically prevents that from happening because it dampens the ability for a "speedup" wave to propagate.
Of course this is all impossible for humans. All it takes is a few idiots to throw off the balance.
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so even in traffic it should be like 5+ car lengths even though you are going slow.
Other drivers: "It's free real estate"
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Secret is to play the game next to a semi. Some semis kinda do it too by engine braking as they see the wave approaching instead of waiting until theyre close to even slow
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So basically: 1. Put people in public transport away from the steering wheel, 2) scale back cars use.
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Go back to fuckcars with the rhetoric.
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Yep! All it takes is one person braking, and then the person behind braking, then the person behind them, and eith each braking the overall speed slows down more and more. It creates a wave of traffic. The wave passes through. The starting point I think moves back further and further.
I think about it a lot while I sit in traffic.
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"Pick a lane and stay in it" leads to slow drivers blocking the left lane, no?
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99% of traffic like this is caused by people following too closely.
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Yeah ideally you put 3 seconds between you and the car in front of you. Gives a nice, springy cushion to not brake as much. Your mechanic will also be surprised how much longer your brakes last.
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I've always said that if you're using your brakes on the highway and it's not for an emergency stop, you're too close to the car in front of you. Even if they're the type that are on and off the brake constantly, if their speed isn't changing much you shouldn't need to follow their example. Of course I try to get out from behind them because they are like crying wolf and one of those brakes might be for real.
When caught in a traffic jam I look for a semi to get behind. They won't accelerate fast like some car drivers do, and they don't stop as fast either. Plus they can see better if things area really starting to move or not. Keep a few car lengths behind them and while everyone is doing the start and stop motions, I'm keeping a slow but steady speed usually without needing to brake at all. It's also less stressful.
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Too many people were taught, and still teach, the "two car's length" rule. Which is awful. 2 to 3 seconds is much better and intuitive to figure out.
You say 3, which is great, but I'd settle for 2. Most people on the highways around me leave more like 0.5; I sincerely think the vast majority of people greatly overestimate the amount of space in front of them to the next car.
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If you're in traffic (i.e. if you are part of the traffic) and you leave a 3 second gap between you and the car in front of you, another car will drive into that gap. If you back off to create another 3 second gap, it will happen again. Even worse, if you hit the brakes to create that three second gap, even if it's very lightly, you might cause an even worse traffic jam behind you.
I would prefer to leave a big gap to the traffic in front of me, but in many cases 3 seconds simply isn't practical. A car merging into the lane in front of you is inherently more dangerous than a car already being in that lane. If you keep trying to maintain a 3 second gap in heavy traffic, not only do you put yourself in more danger as you keep having cars merging in front of you, you also cause more danger to the drivers behind you by constantly backing off or braking to try to maintain a gap.
It would be absolutely wonderful if everybody believed in the 3 second rule. Traffic would flow so much more smoothly. But, apparently that isn't human nature. And, if you keep fighting for that gap when nobody else believes in it, you can actually make things less safe for yourself and for others.
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It's the people not zipper merging correctly. You have idiots entering that are not up to speed and you have idiots breaking for the idiots not up to speed.
On ramps should be required to have their lane not end abruptly which causes the panic. The on ram should continue for at least a 1/4 mile.
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Cars cause traffic. Cars changing lanes causes traffic. Cars merging causes traffic. Only solution, get rid of the cars and the system built to cater to them.
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I've literally seen a test with 4 cars driving around a circle, and they tell the drivers, "go at a consistent speed and maintain the distance in front of you" and after 5 minutes they're all bunched up on one side of the circle. No amount of zipper merging and nice ramps will fix this.
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Adding to this, more collector-distributor roads that parallel the highway on both sides to reduce the weaving of people entering and exiting.
This is also why I hate cloverleaf highway intersections, the merge period is way too short and the speed delta can be high.
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Just one more road bro it will fix traffic
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people not zipper merging correctly
Zipper merging is more complicated than driving straight forward and requires both lanes to slow down significantly relative to the cars in front and behind them.
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The best flowing highways I've ever seen were ones where the on ramp didn't end, but became the off ramp for the next exit. Obviously you can't have that everywhere, but it's basically a free flow lane that gives time for adjustment. I've also seen on ramps (older ones) that aren't much more than a turn lane, and dangerous if you don't know the area and traffic patterns.
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The issue with this style of lane design is it basically doubles the amount of lane changes that lane experiences, which can make it the most dangerous possible space if exits are close together. I've lived around Dallas. It's scary.
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My area kinda has this except the on ramp ends quickly merging into the right lane, then the off ramp starts almost immediately after. It makes traffic worse as cars trying to get on cannot merge effectively because cars want to be in that lane to exit. I find the best flow is having the off ramp before the on ramp, which minimizes right lane conflicts.
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idiots breaking
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CGP grey did a video on it: https://www.youtube.com/watch?v=iHzzSao6ypE
Basically one car breaking too much will make the following brake even more and so on until one stops and there's a jam. There is no clear reason like a road blockage or an accident, just compounding slow down.
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Basically one car breaking too much will make the following brake
If the car in front of me started breaking, I'd definitely get out of the way.
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I'd recommend this video as a response to that one, cgp greys video is technically correct and fucking dumb at the same time
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3 fucking seconds
The answer is a simple 3 second gap.
That's it, just 3-mississippi (or 3-onethousand) seconds behind the car in front of you and most of the avoidable jams go away.
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If you do that, someone will move into the gap. If someone moves into the gap you can slow down to make another gap to them, but then someone else will drive into that gap. I don't know of any major city where you can maintain a 3 second gap during rush hour.
Even worse, if you ever brake to try to create a gap, you're likely to cause a traffic jam behind you.
Sure, if everybody did follow the suggestion and allowed a 3 second gap you wouldn't have traffic jams, but that's just not human nature, apparently.
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You attribute an uneducated, uncivil approach to human nature, but I have been in human queues around the world, and they vary hugely based on cultural and social differences.
What you think is human nature seems to actually be driving culture in your region.
Yesterday I had a swasticar driver actually let me in on a disorderly merge. I was amazed, it was a first. Clue: nothing about Hondas changes people to be better. Tesla and BMW drivers are just shittier at sharing. This is culturally allowed.
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You're totally right. It's a social/culture issue. You doing this on your own isn't going to do shit. Everyone has to miraculously decide to come together to solve the problem with no one taking advantage. It's the same reason we can't do anything about climate change.
Edit: I realize this came off as extremely dismissive about climate change. I still think we should do what we can to, at the very least, reduce effects. It was more just a realistic take of why I think we're all fucked. I still avoid eating meat, single use garbage, and other wasteful shit, don't get me wrong.
Can anyone tell me why this is being downvoted? I don't really care about downvotes, Im more just wondering how I'm wrong.
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Except the person next to you or behind you gets frustrated and cuts you off and you have to hit the brakes and create a traffic pulse.
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Well yes, society functions only with cooperation. Uncivil behaviour ends with violence and dismay.
However 3s usually allows for slow adjustments which alleviate caterpillaring.
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The people at the front are morons and probably in the wrong lane.
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You don't like driving 55 in the passing lane? You get such a great view of everyone flipping you off!
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It's usually a complex crowd effect created by many participants trying to maneuver among each other in slightly disperate ways.
In Portland OR, it really is because some dingbat slowed down to 20 MPH on the interstate for literally no fucking reason at all.
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Taking I-5 into Vancouver from Portland is always horrific. Once you get over the bridge it always clears right up! A big part of that is all the on ramps. There's so many of them! So everybody is having to make way every 10 feet for someone merging in.
It's horrendous.
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Yeah they could probably stand to lose the more southern of the two ramp sets at Delta Park, feels very extra and overall unhelpful (And I say this as someone who uses that ramp when headed north). Of course ODOT's solution, beyond replacing the bridge, is to widen I-5 south of the bridge - Which anyone with a brain and 50 years of highway traffic studies can tell us would directly contribute to worsening the problem.
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Often they do this because their car is barely limping along and they are trying to make it to the next exit.
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This driver is distinct from that driver. We definitely have those too, and they have my sympathies. 10 seconds of engine death vs 10 seconds of brain death.
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It all starts with someone in the passing lane, not passing, and one or more pissed off people behind them :)
The pissed off people trying to get around causes the wave of people behind them to brake and it snowballs from there.
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Yeah I drive around 3 hours on the highway every several weeks. Sometimes on my drive, there's obviously traffic. A lot of times it will be something like rush hour traffic, a crash, construction, etc.
But then like...a good portion of the time when I come to the very front of the "clog", I find that it is just a blockade of multiple people going incredibly slowly and taking up all lanes of traffic, refusing to move over despite the fact that they are going under the speed limit.
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Exactly, it's entirely because the people in front of you are going slow.
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People drive too close to each other, someone has to slow down and then the car behind slows down a bit more. Repeat until you get to the point someone completely stops. Then the next car stops for slightly longer.
If you leave a safe distance then it wouldn't happen.
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Its because of two things. One is that people hog the passing lane or try to pass slowly so it takes them a few minutes to overtake a few cars, and also because people drive at different speeds. Some people drive at the speed that feels comfortable, others drive the state imposed speed limit. This creates pockets of dense traffic, and then people try to pass, but there is always the person who tries to pass as slow as possible because they are going a few mph over the speed limit.
Its really just a bad combination of laws, and drivers who are terrified of breaking the law, and people who dont know how to drive correctly in a way to reduce traffic. Also many people are just never consider that others also need to use the roads. They don't care about traffic. Some people also have health issues, like blindness, or mental handicaps, which means driving at interstate speeds is about all they can muster.
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Hey, if you have some physical limitation and cannot or are simply not comfortable going faster, that's 100% fine (assuming you can operate a car safely). Stay the hell in the right lane and never leave it, thanks
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Years ago I was in LA on business and ended up on I-5. All of a sudden traffic stopped dead. Eventually people were getting out of their cars and walking around. About a half-hour later, traffic started up again. We never saw what was responsible for the blockage. No wreckage, no obvious marks or debris on the pavement, nothing. I'm glad I live in a small city nowhere near California.
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https://www.mdpi.com/2076-3417/11/9/4278
TLDR: modeling traffic as a gas leads to fairly accurate predictions. If that doesnt mean anything to you, here's a decent visualization of how gasses move around in a system. In this analogy, each of the gas particles models a car on the road. https://youtu.be/Hr5Baj3lXFA
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Bumper riders Lane switchers Brake checkers Ramp users switching lanes wayyy too late
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George Carlin explains it pretty simply
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You are thr traffic.
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basically it's a thing with cars where if a single car slows down for any reason, even slightly, it causes a cascade effect that leads to traffic jams.
Yet another reason why cars suck.
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It's all a mad rush of people trying to get to where they don't want to be as fast as possible
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Idk why they call it a bottleneck, when it's a straight line through the opening of the bottle.
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Similar to https://en.m.wikipedia.org/wiki/Turbulence The gist of it is that once you reach critical density people can not drive homogenously anymore and (de-) accelerate constantly to not bump into the next car. The problem could be alleviated with self driving cars which negotiate a uniform speed.
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The problem is solved by connecting all the cars, and putting them on rails that are electrified. This way you move fuel off site, and the cars are synced by the connection.
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I was always dreaming about some kind of "individual public transport" (I think minority report had a nice example, because there the transport is part of your flat and thus doesn't waste space when not moving), which interconnects into trains for longer distances. Currently it would probably be only freezable for Intercity ranges, otherwise the coupling process takes longer than the drive.
Also, you can charge electric cars through induction rings in the street, like mobile phones. The efficiency is not the best though.
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The problem could be alleviated with self driving cars which negotiate a uniform speed.
Other than the obvious public transit solution comment, you are aware that ACC exists right?
We literally have the technology on almost all new cars to keep a uniform distance from the car in front of it. Even without that if people realized you can save fuck all time by speeding on your 30 mile commute we could have cars moving at the speed limit and just have smooth traffic flow without any need for self-driving
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Geez... I didn't want to write an entire essay and just mentioned ONE possible example for improvement, to illustrate my explanation. No need to get salty...
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Your solution is a dream. Real solutions already exist, it's called mass transit.
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It exists... Only in movies and games though;)
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self driving cars which negotiate a uniform speed.
Until then, human drivers could approximate this system by all agreeing on a uniform speed. Maybe through some sort of app?
Or, this sounds crazy, perhaps the authorities could post signs by the side of the highway with the uniform speed printed on it?
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That is actually a thing, but the optimal speed depends on traffic. Otherwise it always helps to lower speed limits, there are several studies in my area which show that on average everybody would arrive quicker at their destination if we reduce urban speed limit from 50 to 30 km/h.
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This is like saying you don’t know how a bottleneck works.
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Reaction times of humans.
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Traffic is a "thing" because the slowest common perambulator is always in front
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slow speeds cause accidents, not speed, it it the sudden stop, the cause of some inbred driver
170 comments